1. Field of the Invention
The present invention relates to compositions useful in treating hyperpigmentation of human skin. Further, the present invention relates to methods of applying the compositions to the skin to effect treatment.
2. Description of the Prior Art
Human skin color is determined primarily by the content of the pigment melanin in the basal epidermis layer. Melanin is synthesized by the process of melanogenesis within melanocytes (pigment-producing cells). Melanin is deposited onto melanosomes, which are transferred to keratinocytes in the basal epidermal layer. Melanosomes present in these basal keratinocytes are the key determinants of skin color. The keratinocytes leave the basal layer and undergo differentiation forming the cornified top layer of the skin. Once the keratinocytes leave the basal layer, the melanosomes lose their characteristic electron dense structure, and the load of melanin is carried to the surface of the skin by the differentiating keratinocytes.
The skin can become hyperpigmented when too much melanin concentrates at one area or portion of the skin due to the retention time of the melanosomes in the basal layer. Hyperpigmentation can also occur as a result of overexposure to the sun or other inflammatory stimuli. Hyperpigmentation can take the form of solar lentigines (age spots), ephilides (freckles), melasma, chloasma, and pigmented keratoses.
The prior art discloses ways to treat hyperpigmentation by application of skin lightening agents. Representative skin lightening agents include hydroquinone and Vitamin C. Such agents typically lighten the skin by inhibiting the expression of tyrosinase enzymes involved in melanogenesis.
It would be desirable to have a way to treat hyperpigmentation by application of agents that reduce the ability of epidermal cells to retain melanin. A reduction in ability to retain melanin would speed the transfer of the melasonomes to the keratinocytes and allow existing hyperpigmented portions of the skin to be lightened or de-pigmented faster than with conventional skin lightening agents, which act primarily to inhibit the formation of new melanin.
It is an object of the present invention to provide a composition and method for treating, preventing and/or ameliorating hyperpigmentation of human skin.
It is still another object of the present invention to provide such a composition and method that has one or more agents that decrease the retention time of melanosomes at the basal layer. This is achieved by inhibiting the ability of epidermal cells to retain or uptake melanin/melanosomes and/or increase the rate of transport of basal keratinocytes to the surface of the skin.
These and other objects of the present invention are achieved by a method and composition that comprises (a) a de-pigmenting agent in an amount effective to prevent, treat and/or ameliorate pigmentation at an area of skin to which it is applied, and (b) a cosmetically or pharmaceutically acceptable vehicle. Suitable de-pigmenting agents include 3,3xe2x80x2-thiodipropionic acid, thiazolidine-2-carboxylic acid, Kaempferol-7-glucoside, perilla oil, and clofibrate and clofibrate analogs and/or derivatives, as well as those set forth below.